Currently, on construction sites, a lift is mounted along a wall of a building or down a shaft. A scaffolding height is meant to increase as a construction height increases. In order to easily raise and lower the necessary materials and/or workforce for construction purposes, the scaffolding comprises a lifting assembly. The lifting assembly is equipped with at least one rack mast. The mast can be gradually mounted as the building rises or once the structural framework has been completed. A motorised platform can be moved vertically along the rack mast, and can thus have varying heights on the said mast. The platform is powered by a power unit including at least one motor block and at least two roller boxes. The power unit is guided along the rack mast. The platform is fixed to the power unit which lifts it and guides it along the said rack mast.
The power units known today are of the monoblock type. By “monoblock” is meant the motor block, fulfilling the power function, and the roller box, fulfilling the guiding function, together forming a single and same unit. The power function can not be dissociated from the guiding function.
Moreover, this monoblock power unit has a specific structure which changes according to the platform to be lifted and according to the rack mast along which it is guided. Indeed, the bulk of the base plate of an elevator, of a working platform, of a load hoist, or of a materials' hoist, is not the same. Each one of these lifting assemblies must, therefore, be placed differently in relation to the mast on the one hand, and to the power unit on the other.
For example, in the case of a load hoist, the load plate of the said load hoist is interlocked with a rack mast through the intermediary of a power unit. A section of the mast carrying the rack is directed outwards in relation to the construction along which the load hoist is mounted, and extends in a plane, parallel to a plane of the construction. The load plate is hung onto a lateral side of the power unit, i.e. the power unit is located next to the load plate. The load plate cannot be positioned on the side hosting the motors due to the bulk of the latter and the necessity for the load plate to descend as near to the ground as possible.
In the case of a construction-site elevator, the platform for the said elevator is interlocked with a rack mast through the intermediary of a different power unit. The section of the mast carrying the rack is directed outwards in relation to the construction along which the elevator is mounted, but extends in a plane perpendicular to a plane of the construction. The platform is hung underneath the power unit. Indeed, a construction site elevator transports heavy-weight material. It is thus advantageous if the platform of the construction-site elevator is able to touch the ground when the said elevator is in the lower position on the rack mast in order to facilitate the loading of the said elevator, for example using a hand truck or a fork-lift truck.
In the case of a self-elevating platform, the base plate is also hung onto the lateral sides of the power unit. However, the section of the mast carrying the rack extends in a different plane than the mast carrying a load hoist. Hence, in this case, the power unit also has a different structure.
It is, therefore, not currently possible to use a same power unit enabling on a construction site, for example, the elevation along a mast of a construction-site elevator, a rack platform, a rack lift or other such type. Depending on the position of the mast section which holds up the rack and depending on the lifting device concerned, the overall structure of the power unit changes.